1. Field of the Invention
The present invention relates to a wireless power supply technique.
2. Description of the Related Art
In recent years, wireless (contactless) power transmission has been receiving attention as a power supply technique for electronic devices such as cellular phone terminals, laptop computers, etc., or for electronic vehicles. Wireless power supply transmission can be classified into three principal methods using an electromagnetic induction, an electromagnetic wave, and an electric field/magnetic field resonance.
The electromagnetic induction method is employed to supply electric power at a short range (several mm or less), which enables electric power of several hundred watts to be transmitted in a band that is equal to or lower than several hundred kHz. The power use efficiency thereof is on the order of 60% to 98%.
In a case in which electric power is to be supplied over a relatively long range of several meters or more, the electromagnetic wave reception method is employed. The electromagnetic wave reception method allows electric power of several watts or less to be transmitted in a band between medium waves and microwaves. However, the power use efficiency thereof is small. The electric field/magnetic field resonance method has been receiving attention as a method for supplying electric power with relatively high efficiency at a middle range on the order of several meters (see Non-patent document 1).